virtio-net: add missing virtqueue kick when flushing packets

We tends to batch submitting packets during XDP_TX. This requires to
kick virtqueue after a batch, we tried to do it through
xdp_do_flush_map() which only makes sense for devmap not XDP_TX. So
explicitly kick the virtqueue in this case.
Reported-by: NKimitoshi Takahashi <ktaka@nii.ac.jp>
Tested-by: NKimitoshi Takahashi <ktaka@nii.ac.jp>
Cc: Daniel Borkmann <daniel@iogearbox.net>
Fixes: 186b3c99 ("virtio-net: support XDP_REDIRECT")
Signed-off-by: NJason Wang <jasowang@redhat.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/virtio_net.c

@@ -1269,7 +1269,9 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 {
 	struct receive_queue *rq =
 		container_of(napi, struct receive_queue, napi);
-	unsigned int received;
+	struct virtnet_info *vi = rq->vq->vdev->priv;
+	struct send_queue *sq;
+	unsigned int received, qp;
 	bool xdp_xmit = false;
 
 	virtnet_poll_cleantx(rq);
@@ -1280,8 +1282,13 @@ static int virtnet_poll(struct napi_struct *napi, int budget)
 	if (received < budget)
 		virtqueue_napi_complete(napi, rq->vq, received);
 
-	if (xdp_xmit)
+	if (xdp_xmit) {
+		qp = vi->curr_queue_pairs - vi->xdp_queue_pairs +
+		     smp_processor_id();
+		sq = &vi->sq[qp];
+		virtqueue_kick(sq->vq);
 		xdp_do_flush_map();
+	}
 
 	return received;
 }